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- Gutierrez Albarran, M. L., et al.
(författare)
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The Gaia-ESO Survey : Calibrating the lithium-age relation with open clusters and associations I. Cluster age range and initial membership selections
- 2020
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 643
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Tidskriftsartikel (refereegranskat)abstract
- Context: Previous studies of open clusters have shown that lithium depletion is not only strongly age dependent but also shows a complex pattern with other parameters that is not yet understood. For pre- and main-sequence late-type stars, these parameters include metallicity, mixing mechanisms, convection structure, rotation, and magnetic activity.Aims: We perform a thorough membership analysis for a large number of stars observed within the Gaia-ESO survey (GES) in the field of 20 open clusters, ranging in age from young clusters and associations, to intermediate-age and old open clusters.Methods: Based on the parameters derived from the GES spectroscopic observations, we obtained lists of candidate members for each of the clusters in the sample by deriving radial velocity distributions and studying the position of the kinematic selections in the EW(Li)-versus-T-eff plane to obtain lithium members. We used gravity indicators to discard field contaminants and studied [Fe/H] metallicity to further confirm the membership of the candidates. We also made use of studies using recent data from the Gaia DR1 and DR2 releases to assess our member selections.Results: We identified likely member candidates for the sample of 20 clusters observed in GES (iDR4) with UVES and GIRAFFE, and conducted a comparative study that allowed us to characterize the properties of these members as well as identify field contaminant stars, both lithium-rich giants and non-giant outliers.Conclusions: This work is the first step towards the calibration of the lithium-age relation and its dependence on other GES parameters. During this project we aim to use this relation to infer the ages of GES field stars, and identify their potential membership to young associations and stellar kinematic groups of different ages.
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| 2. |
- Bonito, R., et al.
(författare)
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The Gaia-ESO Survey : A new diagnostic for accretion and outflow activity in the young cluster NGC 2264
- 2020
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 642
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Tidskriftsartikel (refereegranskat)abstract
- Context. NGC 2264 is a young cluster whose accretion properties can be investigated in detail by taking advantage of the FLAMES data in the context of the Gaia-ESO Survey. In fact, the analysis of the Hα emission line profile can provide us with information about the accretion and ejection activity of young stars. However, a strong nebular emission that contributes to the Hα emission can alter the profiles, with consequences for their physical interpretation. Aims. Our study is aimed at investigating the accretion and ejection properties of NGC 2264 by applying a proper treatment of the sky contribution to the Hα and forbidden emission lines (FELs; [SII] and [NII] doublets). Methods. We developed a tool, the OHαNA-method, to handle the strong nebular contribution and spectra with spurious profiles of the Hα and FELs, namely altered Hα profiles or absorption features artificially created where emission lines (FELs) are expected. We derived the quantitative measurements of relevant parameters to describe the accretion and ejection processes in young members of NGC 2264, focusing on reliable quantities derived from the width of the lines, which is relatively unaffected by the nebular emission, unlike the intensity peak, which can be altered significantly. Results. We derive the quantitative measurements related to the Hα emission line and discuss the comparison between the original and sky-subtracted spectra. We thus reveal possible profile alterations with consequences for their physical interpretation. Furthermore, we show the analysis of the variability for multi-epoch observations, also deriving the velocity of the infalling and outflowing plasma from the wings of the broad Hα emission line (in accreting stars). We also explore the mass accretion rate versus full width at zero intensity of the Hα line, namely M versus FWZI(Hα), a correlation based on the width of the emission line, which is expected to be more robust with respect to any measurement derived from the peak (e.g., Hα10%) and possibly altered by the nebular contribution. Conclusions. We are able to ascertain that more than 20% of the confirmed accretors, which have already been identified in NGC 2264, are affected by the alteration of their line profiles due to the contribution of the nebular emission. Therefore, this is an important issue to consider when investigating accretion and ejection processes in young stellar clusters. While a small fraction of spectra can be unequivocally classified as either unaffected by nebular emission or dominated by nebular emission, the majority (> 90%) represent intermediate cases whose spectral features have to be investigated in detail to derive reliable measurements of the relevant parameters and their physical implications.
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